There is substantial literature in the art with respect to the hydrogenation of aromatic amines, e.g., methylenedianiline to produce 4,4'-methylenedi(cyclohexylamine) often referred to as PACM.
Some of the early hydrogenation work to produce PACM was done by Whitman and Barkdoll, et al. and their work is set forth in a series of U.S. patents, e.g., U.S. Pat. Nos. 2,511,028; 2,606,924; 2,606,925; and 2,606,928. Basically the processes described in these patents involve the hydrogenation of methylenedianiline at pressures in excess of 200 psig, preferably in excess of 1,000 psig, at temperatures within a range of 80.degree. to 275.degree. C. utilizing a ruthenium catalyst for the hydrogenation. The hydrogenation is carried out under liquid phase conditions by using an inert organic solvent in the hydrogenation process. Examples of ruthenium catalysts utilized for the hydrogenation process include ruthenium oxides such as ruthenium sesquioxide and ruthenium dioxide.
Brake, et al. continued in the development of processes for manufacturing PACM by hydrogenating methylenedianiline. They found that if the ruthenium was carried upon a support and the support was alkali-moderated, the catalyst was much more active and catalytically effective in producing the desired hydrogenated PACM product. Alkali moderation was effected by contacting the catalyst and support with alkali metal hydroxide or an alkoxide; also, such alkali moderation of the catalyst could be effected prior to hydrogenation or in situ during the hydrogenation.
Representative patents showing the utilization of alkali moderated ruthenium catalysts to hydrogenate methylenedianiline include U.S. Pat. Nos. 3,636,108; 3,644,522; and 3,697,449. Alkali metal and alkaline earth metal nitrates and sulfates have similarly been shown effective in U.S. Pat. No. 4,448,995 under high pressure (4000 psia) hydrogenation conditions. Representative supports in the '449 patent include bauxite, periclase, zirconia, titania, diatomaceous earth, etc.
Other catalysts have been utilized for the hydrogenation of methylenedianiline and examples are shown in U.S. Pat Nos. 3,591,635 and 3,856,862. Both disclose the use of a rhodium component as a catalytic material and each require the use of an aliphatic alcohol as a solvent. The rhodium is alkali moderated using ammonium hydroxide as a pretreatment or by carrying out the reaction in the presence of ammonia. European application 66,212 discloses the use of rhodium on alumina to obtain 15-40% trans,transisomer ratio but again the pressures are high (4000 psia).
U.S. Pat. No. 4,376,724 discloses a catalyst with rhodium present in the surface layer of particles of silica or titania which is alleged as being suited for the synthesis of oxygen containing compounds and various hydrogenation reactions including the nuclear hydrogenation of aromatic compounds and in the hydrogenation of unsaturated bonds of olefins, nitriles, etc. The catalyst is prepared by dipping the support into an aqueous solution of a water soluble rhodium salt adjusted to a specific pH followed by drying and reduction. The supports include silica or titania as a single component.
U.S. Pat. Nos. 4,960,941 and 5,026,914 disclose a process for the hydrogenation of aromatic amines utilizing a catalyst comprising rhodium on titania or zirconia. To enhance attrition resistance titania and/or zirconia chemically bound to silica was used as a support for the rhodium.
U.S. Pat. No. 4,754,070 discloses a process for hydrogenation methylenediamiline using a mixed metal catalyst of rhodium and ruthenium carried of a variety of supports, alumina and diatomaceous earth.